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* [glibc] Linux: Use rseq in sched_getcpu if available
@ 2020-07-06 9:13 Florian Weimer
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From: Florian Weimer @ 2020-07-06 9:13 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6e29cb3f61ff5432c78a1c84b0d9b123a350ab36
commit 6e29cb3f61ff5432c78a1c84b0d9b123a350ab36
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon Jul 6 10:21:31 2020 +0200
Linux: Use rseq in sched_getcpu if available
When available, use the cpu_id field from __rseq_abi on Linux to
implement sched_getcpu(). Fall-back on the vgetcpu vDSO if unavailable.
Benchmarks:
x86-64: Intel E5-2630 v3@2.40GHz, 16-core, hyperthreading
glibc sched_getcpu(): 13.7 ns (baseline)
glibc sched_getcpu() using rseq: 2.5 ns (speedup: 5.5x)
inline load cpuid from __rseq_abi TLS: 0.8 ns (speedup: 17.1x)
Diff:
---
sysdeps/unix/sysv/linux/sched_getcpu.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
index c019cfb3cf..c0f992e056 100644
--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
@@ -18,10 +18,12 @@
#include <errno.h>
#include <sched.h>
#include <sysdep.h>
+#include <atomic.h>
#include <sysdep-vdso.h>
+#include <sys/rseq.h>
-int
-sched_getcpu (void)
+static int
+vsyscall_sched_getcpu (void)
{
unsigned int cpu;
int r = -1;
@@ -32,3 +34,19 @@ sched_getcpu (void)
#endif
return r == -1 ? r : cpu;
}
+
+#ifdef RSEQ_SIG
+int
+sched_getcpu (void)
+{
+ int cpu_id = atomic_load_relaxed (&__rseq_abi.cpu_id);
+
+ return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu ();
+}
+#else /* RSEQ_SIG */
+int
+sched_getcpu (void)
+{
+ return vsyscall_sched_getcpu ();
+}
+#endif /* RSEQ_SIG */
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